In fabricating a multi-layered semiconductor device, as a method of reducing a parasitic capacitance of an interlayer insulating film formed on a semiconductor wafer (hereinafter, referred to as a “wafer”) used as a substrate, to improve an operation rate, it is known to use a porous low-k film. This kind of film may include, for example, an SiOC film containing silicon, carbon and oxygen and having Si—C bonds. In order to cause a wiring material such as copper to be embedded, the SiOC film is etched by plasma of a CF-based gas, e.g., CF4 gas, using a resist mask and a lower layer-side mask, and an ashing process is then performed on the resist mask by plasma of oxygen gas.
However, in the case where a plasma process such as the etching or the ashing is performed on the SiOC film, for example, the Si—C bonds in an exposed surface of the SiOC film exposed to the plasma, i.e., in sidewalls and bottom surfaces of recesses, are broken by the plasma, so that C is desorbed from the film. Since Si with unsaturated bonds created by the desorption of C is unstable in this state, Si is bonded with, for example, moisture in the atmosphere or the like, resulting in Si—OH.
Such a plasma process causes a damaged film to be formed on the exposed surface of the SiOC film. In such a damaged film, the content of carbon is lowered. This increases permittivity of the damaged film. As miniaturization of a line width of a wiring pattern and thinning of a wiring layer, an insulating film or the like are progressing, and the proportion of an influence of the surface portion on the entire wafer is being increased. Even in the surface portion, the increase in the permittivity of the surface becomes one of factors causing properties of the semiconductor device to be deviated from the designed values. In addition, although the mask used for etching the SiOC film is removed by generating the plasma as described above, it is preferable to remove the mask by a simpler method.
For example, there is known a technique of preliminarily embedding PMMA (acrylic resin) in pores of a porous low-k film formed on a substrate, performing a certain process such as etching on the low-k film, heating the substrate, supplying solvent to the substrate, and additionally supplying microwave to remove the PMMA. However, the removal of the PMMA requires a long time of about 20 minutes by using plasma. In addition, the substrate is required to be heated up to a temperature of 400 degrees C. or higher. Therefore, there is a problem that elements which have already been formed on the substrate are likely to be adversely affected.